The present disclosure relates to an image reading device that is used in digital copies, image scanners, and the like and that scans a document to read it, and to an image forming apparatus incorporating such an image reading device.
Conventionally, in copiers of a mirror scanning type and the like, an image reading device of a flatbed type is widely used in which a document is placed on a contact glass fixed on a document stage of a document reading part and an image of the document is read while a carriage arranged under the contact glass and incorporating a light source and a mirror is moved (for scanning) parallel to the face of the document by a predetermined driving device.
In such an image reading device, a document is irradiated with light by use of two light sources arranged at opposite sides of a reading region from each other in the sub scanning direction, and reflected light (image light) from the document is converged through a lens to be imaged on a sensor face of a CCD or the like; thereby image data is read out. On the other hand, with the spread of LEDs (light emitting diodes) in recent years, as a light source in the image reading device, a side light type is used that is composed of a cylindrical light guide and LEDs arranged at an end part of it in the longitudinal direction.
For example, there is known an image reading device that includes, as a lighting device, first and second light guides at both ends parts of each of which a pair of first and second light sources are arranged respectively and that controls the light emitting operation of the first and second light sources according to the reading speed and the reading mode, that is, color, black and white, or otherwise. In this method, light is shone into the light guides through their end parts in their longitudinal direction so as to illuminate the document over its entire range in the main scanning direction, and thus there is no need for a large number of LEDs; this helps produce lighting devices at low cost. On the other hand, inconveniently, light from an LED is shone into a light guide through one end part of the light guide, and thus the light leaks from the light guide through its other end part.
To avoid that, a method is used which prevents leakage of light with a reflection member such as aluminum tape provided on an end face of the light guide opposite from the LED. For example, there is known a lighting device that includes a light guide in the shape of a bar, a light source part arranged at one end of the light guide, and a reflector arranged at the other end of the light guide.